This invention relates to a seal assembly for a rotary machine part, particularly a pump impeller for a liquid pump. The assembly includes the pump impeller mounted on a pump shaft by means of an impeller hub, a counter ring cooperating with the impeller, a slide ring seal as well as a connecting body axially holding together components of the seal assembly.
German Pat. No. 2,729,928 discloses a centrifugal pump including an integrated seal unit. An impeller made of steel or fiber-reinforced synthetic material is affixed to a hub made of a thick-walled sintered steel or metal. A counter ring is arranged on the free end of the hub with the interposition of an elastomer member. A connecting body extends axially from the free end of the hub beyond the far end of the slide ring seal. The connecting body is made of metal or is formed from the elastomer counter ring. It is a disadvantage of this known construction that the relatively compact impeller-and-hub connection has a relatively large weight and thus represents an appreciable manufacturing expense. It is a further disadvantage of this known structure that it is not possible to integrate the counter ring-which often is made of brittle material, such as ceramics--in the impeller to thus obtain an axially shorter structural unit. Further, in the known structure an additional connecting body--made of an elastomer or metal--is (and necessarily has to be) provided for connecting either the impeller or the hub with the slide ring seal as a structural unit.
German Offenlegungsschrift (application published without examination) No. 2,623,583 discloses a centrifugal pump, particularly a cooling water pump for automotive vehicles. In this structure, the slide ring seal, the impeller and the counter ring are combined to a structural unit in such a manner that the slide ring seal has a housing which surrounds the counter ring and the counter ring is fixedly connected with the impeller with the intermediary of an elastomer body. The metal impeller, again, is not adapted to receive, directly or with the intermediary of an elastomer layer, the counter ring made of a brittle material. Further, again, a separate connecting part is needed to obtain a unit for installation.
U.S. Pat. No. 3,594,102 discloses a water pump impeller having electrically insulating and anti-corrosion properties. The impeller which is of a synthetic material is, in the zone of its inner circumferential surface, provided with an axially relatively short metal support body and is, by means of a headless screw, fixed radially to the pump shaft. The impeller has an axial extension also made of a synthetic material. A counter ring is positioned in a recess of the impeller by means of an elastic body. If the elastic body were absent and the counter ring were made, for example, of a ceramic material, the non-yielding synthetic material of the impeller could not prevent a heat-caused bursting of the brittle counter ring.